1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device employing an electric field parallel to the substrate, which is called an in-plane-switching (IPS) type.
2. Description of the Related Art
A so-called active matrix liquid crystal display device includes, in each pixel region formed on a surface of a substrate on a liquid crystal side, a thin film transistor which is turned on through supply of a scan signal from a gate signal line and a pixel electrode to which an image signal is supplied from a drain signal line via the turned-on thin film transistor.
A liquid crystal display device called an IPS type has a structure in which a counter electrode is formed on the substrate (TFT substrate) side including the thin film transistor so as to generate an electric field containing a component parallel to the substrate between the counter electrode and the pixel electrode.
A liquid crystal display device of the above-mentioned structure is known to have the pixel electrode and the counter electrode formed, for example, in the following manner. The pixel electrode (or counter electrode) is formed of a planar transparent conductive film which is formed over a substantially entire region of the pixel region. The pixel electrode (or counter electrode) has an insulating film formed thereon, the insulating film covering the pixel electrode (or counter electrode). The counter electrode (or pixel electrode) is formed of a plurality of linear transparent conductive films which are provided in parallel with one another on the insulating film so as to overlap the pixel electrode (or counter electrode).
The IPS type liquid crystal display device as described above may be structured to have an increased aperture ratio of pixels and to excel in wide viewing angle.
In the IPS type liquid crystal display device described above, the film thickness of the liquid crystal layer is formed to be relatively small and is made uniform, to thereby improve the contrast.
To make the film thickness small and uniform, the following technology has been known. According to the technology, at least on the TFT substrate, a resin film which is formed through application so as to cover the thin film transistor is used as a protective film, to thereby flatten a surface of the TFT substrate, and the pixel electrode (or counter electrode) and the counter electrode (or pixel electrode) are formed on a flat upper surface of the TFT substrate.
It should be noted that JP 2004-191557 A, JP 2004-22224 A, and JP 11-65482 A are cited as publicly known documents related to the subject application. JP 2004-191557 A, JP 2004-22224 A, and JP 11-65482 A all describe display devices employing a conductive film which is formed through application. However, the above-mentioned display devices are not intended to include the above-mentioned IPS type liquid crystal display devices.
As described above, in the IPS type liquid crystal display device, there is known a technology of forming the resin film through application in order to make flat the surface of the TFT substrate on a liquid crystal side.
However, it has been pointed out that, in order to further enhance the contrast in the liquid crystal display device, sufficient flatness cannot be obtained only with the above-mentioned resin film.
Further, in the case where the resin film is formed through application, process steps are increased. Therefore, it is desired to attain flatness in the surface of the TFT substrate on the liquid crystal side simultaneously.